The present invention relates to the field of communication and, more particularly, to a device for causing a plurality of images having different optical characteristics to appear through a continuous mirrored screen.
Prior devices for displaying an image through a mirrored surface are described in the following patents: U.S. Pat. No. 569,672 to Wirth; U.S. Pat. No. 720,877 to Bloch; U.S. Pat. No. 2,069,368 to Horinstein; U.S. Pat. No. 2,565,575 to Rosenthal; U.S. Pat. No. 2,698,177 to Engman; and Argentine Pat. No. 193.254, dated Apr. 11, 1973. In such devices, at least one image-bearing transparency or object is located behind a partially transparent mirror of uniform optical density, i.e., a mirror in which transmittance and reflectance are uniform over its surface. The mirrors can be made by any well known mirroring process, such as that involving silver nitrate.
Items displayed through a single, continuous mirror of uniform transmittance must have identical optical properties, including degree of reflectance. It is not possible to display items of different reflectances or physical forms (e.g., two-dimensional transparencies and three-dimensional objects) through a uniform screen because such items require different optical densities to attenuate reflection of environmental light by the items without darkening the images displayed. If the optical properties of the items were different, an item would be visible through the unlighted screen or illuminated to a different intensity than the other items.
The devices of the Wirth, Bloch, Horinstein, Rosenthal and Argentine patents have localized light sources placed directly behind transparencies of two-dimensional images. Such sources provide uneven illumination, detracting from the images displayed and giving rise to "hot spots" which can burn or distort the transparencies.
Therefore, it is desirable in many applications to provide an apparatus for selective display of images having different optical properties within the same mirror, and for illuminating transparencies uniformly without damage to the device or the transparencies.